Significant potential for the treatment of numerous diseases and conditions is offered through the use of progenitor cells and cell-based therapies. Perhaps the most important potential application of human progenitor cells is the generation of differentiated cells and tissues either in vitro or in situ that could be used for cell-based therapies. Today, donated organs and tissues are often used to replace ailing or destroyed tissue, but the need for transplantable tissues and organs far outweighs the available supply. Progenitor cells, directed to differentiate into specific cell types, offer the possibility of a renewable source of replacement cells and tissues to treat numerous diseases including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis, to name only a few examples.
Preliminary research in mice and other animals indicates that bone marrow stem cells, transplanted into a damaged heart, can generate heart muscle cells and successfully repopulate the heart tissue. Other recent studies in cell culture systems indicate that it may be possible to direct the differentiation of embryonic stem cells or adult bone marrow cells into heart muscle cells.
Scientists in many laboratories are trying to find ways to grow adult stem cells in cell culture and manipulate them to generate specific cell types so they can be used to treat injury or disease. Some examples of potential treatments include replacing the dopamine-producing cells in the brains of Parkinson's patients, developing insulin-producing cells for type I diabetes and repairing damaged heart muscle following a heart attack with cardiac muscle cells.
While the utility of stem or progenitor cells holds significant promise in the future of medicine, obtaining sufficient quantities of undifferentiated progenitor cells and maintaining them in an undifferentiated state has been a challenge to biomedical research, as has been controlling the differentiation of progenitor cells in situ into desirable terminal cell types.
During embryogenesis, epithelial cells undergo a change in phenotype into a non-fibroblastic, mesenchymal-type cell in a process called epithelial-mesenchymal transition (EMT). Mesenchymal cells generated during embryogenesis by EMT then give rise to the mesodermal cell types in the embryo, such as skeletal bone, connective tissue of the skin, reproductive organs, cardiac muscle, skeletal muscle, megakaryocytes (red blood cell precursors) and smooth muscle cells. For the purposes of this application, an EMT thereby includes processes wherein epithelial cells undergo either partial or complete change into mesenchymal cells. Associated with this transition is a change in markers characteristic of EMT.